Other actions/effects:

Tramadol suppresses the cough reflex by binding to the mu-opioid receptor binding sites {10}. Due to the high affinity binding of the M1 metabolite to the mu receptor, the metabolite has been found to have more cough suppressant activity than the parent compound {10}.

Unlike morphine, tramadol has not been shown to cause histamine release {01} {08}
But it also has this issue which would explain perhaps why my Zoe kept falling when on it every 8 hours.

The (-) enantiomer is five- to tenfold more potent in NE uptake inhibition and has less affinity for mu receptor binding than for 5-HT uptake {05}. Electrophysiological studies show that tramadol, like morphine, depresses motor and sensory responses of the spinal nociceptive system by a spinal and a supraspinal action {18}. Some opioid activity is derived from low-affinity binding of the parent compound and higher-affinity binding of the mono- O-desmethyltramadol (M1) metabolite to the opioid receptors {01}. The analgesic potency of M1 is about six times greater than that of tramadol in animal models and 200 times more potent in mu-opioid receptor binding {01}.